understand that a hadron may be either a baryon (consisting of three quarks) or a meson (consisting of one quark and one antiquark)

Fundamental Particles: Hadrons

What are Hadrons? 🤔

Hadrons are particles that feel the strong nuclear force. They are made of quarks bound together by gluons. Think of quarks as Lego bricks and gluons as the glue that holds them together.

Baryons (3 Quarks) 🧱🧱🧱

Baryons contain three quarks. Because quarks carry a colour charge (red, green, blue), a baryon’s colours combine to a colour‑neutral (white) particle.

• Proton (\$p\$): \$uud\$
• Neutron (\$n\$): \$udd\$
• Λ⁰ baryon: \$uds\$ (contains a strange quark)

Mesons (Quark + Antiquark) 🎭

Mesons are made of one quark and one antiquark. Their colour and anti‑colour cancel out, leaving a colour‑neutral particle.

• π⁺ meson: \$u\bar{d}\$
• K⁺ meson: \$u\bar{s}\$ (contains a strange quark)
• ρ⁰ meson: \$u\bar{u}\$ or \$d\bar{d}\$ (spin‑1 boson)

Quark Colours & Colour Charge 🔵🔴🟢

Quarks: red, green, blue

Antiquarks: anti‑red, anti‑green, anti‑blue

Rule: Red + Green + Blue = White (colourless)

Key Facts & Analogies 🧩

1. Think of a baryon as a 3‑piece Lego set that must use all three colours to be stable.
2. A meson is like a Lego pair: one brick and its matching anti‑brick.
3. Baryons are fermions (half‑integer spin), mesons are bosons (integer spin).
4. All hadrons are strongly interacting; they can’t exist in isolation without a partner.

Exam Tips & Quick Checks 📚

Remember: Baryon = 3 quarks, Meson = 1 quark + 1 antiquark.

Mnemonic: “Baryon = 3 (big), Meson = 2 (medium).”

Quark flavours: up (u), down (d), strange (s), charm (c), bottom (b), top (t).

Colour rule: Red + Green + Blue = White; Colour + Anti‑colour = White.

Feynman diagrams: Use wavy lines for gluons, straight lines for quarks, dashed for antiquarks.

Examples to recall: Proton (\$uud\$), Neutron (\$udd\$), π⁺ (\$u\bar{d}\$), K⁺ (\$u\bar{s}\$).

Tip: When drawing quark content, label quarks with \$q\$ and antiquarks with \$\bar{q}\$ for clarity.

Check: Verify that the total colour charge is neutral for every hadron you sketch.

Remember the symbols: \$p\$, \$n\$, \$\pi\$, \$K\$, \$\Lambda\$, etc. Use them in your notes and answers.

Quick Reference Table of Quark Flavours

Quick Reference Table of Hadrons